1. Field of the Invention
The present invention relates to a fluid compressor for compressing, e.g., a refrigerant gas in a refrigeration cycle and, more particularly, to a fluid compressor having a spiral blade.
2. Description of the Related Art
Various conventional compressors such as reciprocating and rotary compressors are known. In these compressors, however, the structures of drive units such as crank shafts for transmitting rotational forces to compression units, as well as the structures of the compression units themselves, are complicated, and a large number of components are required. In addition, in order to obtain high compression efficiency, a check valve must be disposed at the discharge side thereof. However, the pressure difference between the inlet and outlet sides of the check valve is large, with the result that gas tends to leak from the check valve. Thus, any conventional compressor has low compression efficiency. In order to solve this problem, dimensional precision of the respective components as well as assembly precision must be improved and, as a consequence, manufacturing costs become high.
In recent years, in order to solve the above problem, there has been provided a fluid compressor having a spiral blade.
A compressor of this type comprises a cylinder, and a rotary rod eccentrically arranged in the cylinder and orbitable relative thereto. A spiral groove is formed on the outer circumferential surface of the rod, along almost the entire length thereof. A spiral blade is fitted in the spiral groove. The outer circumferential surface of the blade is in tight contact with the inner circumferential surface of the cylinder The spiral blade slides in the spiral groove, in the radial direction of the rod, upon the orbital movement of the rod relative to the cylinder.
The space between the rod and the cylinder is partitioned into a plurality of spaces by the blade. The pitches of the spiral groove are gradually narrowed with a distance from one end of the rod. For this reason, the volumes of the plurality of spaces gradually decrease from one end of the rod to the other. Therefore, a fluid flowing from one end of the rod into the spaces is conveyed to the other end of while being confined in the spaces. During this conveyance, the fluid is gradually compressed and finally delivered from the other end of the rod.
In the fluid compressor having the above structure, the overall length of the spiral groove is equal to that of the blade. Each end of the blade abuts against the corresponding end of the groove. For this reason, during the operation of the compressor, the blade is rotated integral with the rod. Since the rod is located eccentric to the cylinder, the speed at which its outer circumference moves is different from the speed at which the inner circumference of the cylinder moves, except at the start of each rotation of the rod and the cylinder. Therefore, the outer circumferential surface of the blade reciprocally slides on the inner circumferential surface of the cylinder in the circumferential direction.
Sliding movement between the blade and the cylinder occurs along the entire length of the blade. A large friction loss occurs between the blade and the cylinder and, as a result, the operation efficiency of the compressor is degraded.